The present invention relates to a filtration structure, in particular a particle filter for the exhaust gases of an internal combustion engine, of the type comprising:                at least first and second filtering elements, each filtering element having an inlet face and a discharge face, connected to each other by at least three lateral faces, said first and second filtering elements having respectively a first and second lateral face arranged opposite each other; and        a seal connecting said faces and extending between said faces;the first lateral face comprising at least a first region that does not adhere, or only slightly adheres to said seal, and extends opposite a first region that strongly adheres to said seal of the second lateral face, said first region that does not adhere or only slightly adheres being delimited by at least a portion of the edge common to the first face and the discharge face.        
Such structures are used in particular in pollution reduction devices for the exhaust gases of internal combustion engines. These devices includes a silencer comprising in series a catalytic purification means and a particle filter. The catalytic purification means is capable of treating polluting emissions in the gaseous phase, while the particle filter is capable of retaining the soot particles emitted by the engine.
In a known structure of the aforementioned type (FR-A-2 833 857), the filtering elements comprise a set of adjacent conduits with parallel axes, separated by porous filtration walls. These conduits extend between the inlet face for the exhaust gases to be filtered and the discharge face for the filtered exhaust gases. These conduits are also closed at one or other of their ends to delimit inlet chambers opening on the inlet face and discharge chambers opening on the discharge face.
These structures operate in a succession of filtration and regeneration phases. During the filtration phases, the soot particles emitted by the engine are deposited on the walls of the inlet chambers. The loss of pressure through the filter increases progressively. Beyond a predetermined value of this loss of pressure, a regeneration phase is carried out.
During the regeneration phase, the soot particles, basically composed of carbon, are burned on the walls of the inlet chambers, using auxiliary heating means, in order to restore the original properties of the structure.
However, soot combustion in the filter does not occur homogeneously. Combustion begins at the front and in the middle of the filter then spreads. Temperature gradients appear in the filter during the regeneration phases.
The temperature gradients inside the filtration structure produce differing local expansion, and consequently longitudinal and transverse stresses in and/or between the various filtering elements.
These pronounced thermomechanical stresses lead to cracks in the filtering elements and/or in the connecting seals between these filtering elements.
To limit the risk of these cracks appearing, the aforementioned application FR-A-2 833 857 proposes the formation on said first face, in the vicinity of said common edge, of a region that does not adhere, or only slightly adheres to the seal, in particular by application of a non-stick coating in this region. The presence of this region allows the thermomechanical stresses in the seal to be released, and if these stresses are too great, the spread of any cracks in the seal to be guided along this region.
Such a structure is not completely satisfactory. In fact, after a number of regeneration phases, cracks may also appear inside a filtering element. These cracks spread substantially in a cracking plane that is transverse to the longitudinal direction of this element. If the lateral faces of the filtering elements also comprise regions that do not adhere, or only slightly adhere to the seal in the vicinity of the discharge face, the cracks also spread in these regions.
Because of this, the downstream portion of the filtering element thus delimited between the cracking plane and the discharge face is no longer held by the seal. This downstream portion is therefore likely to become detached from the filtration structure and be carried away in the downstream direction in the discharge line.